1. Field of the Invention
The present invention relates to an optical signal processor capable of multiplexing/demultiplexing multi-wavelength light.
2. Related Background Art
An optical signal processor disclosed in the specification of U.S. Pat. No. 5,311,606 is known as an optical signal processor capable of multiplexing/demultiplexing multi-wavelength light. The optical signal processor disclosed in this specification includes first and second diffraction grating elements. A diffraction grating element is used as a spatial wavelength branch means which receives light that has propagated through a space and diffracts the light at angles corresponding to wavelengths, thereby spatially branching the light components of the respective wavelengths. When the optical signal processor is used as an optical demultiplexer, wavelength-multiplexed light is diffracted by the first diffraction grating element to branch the wavelengths. The branched light components of the respective wavelengths are diffracted by the second diffraction grating element again and output in parallel. When the optical signal processor is used as an optical multiplexer, light components of the respective wavelengths are diffracted by the second diffraction grating element first. Then, the diffracted light components are diffracted by the first diffraction grating element again and multiplexed.
In the optical signal processor, if the relative position between the plurality of diffraction grating elements is deviated from the design value, no desired optical characteristics can be obtained. To prevent this, it is essential to accurately position each of the plurality of diffraction grating elements at the time of assembly. However, in the conventional optical signal processor, the elements are hard to accurately position, resulting in high manufacturing cost.
The present invention has been made to solve the above problem, and the objective of the present invention is to provide an optical signal processor having desired optical characteristics.
An optical signal processor of the present invention is characterized by comprising a transparent member, which has a first surface and a second surface parallel to the first surface, first spatial wavelength branch means, which branches a light input thereto into light components of different wavelengths and is formed on the first surface, and second spatial wavelength branch means, which outputs the branched light components in parallel to each other and is formed on the second surface.
According to this optical signal processor, the input light is wavelength-branched by the first spatial wavelength branch means formed on the first surface of the transparent member. The branched light components of the respective wavelengths are output in parallel by the second spatial wavelength branch means formed on the second surface parallel to the first surface. This optical signal processor can operate as an optical demultiplexer, an optical multiplexer, or a dispersion adjusting device. Since the first and second spatial wavelength branch means are formed on the surfaces of one transparent member, the two means can easily be accurately positioned. For this reason, an optical signal processor having desired optical characteristics can easily be achieved.
In the optical signal processor of the present invention, the transparent member is preferably made of silica glass. In this case, the optical loss in the transparent member is small. Also, the transparent member is preferably made of a plastic. In this case, replicas can be formed using a mold, and transparent members can be mass-produced at a low cost.
In the optical signal processor of the present invention, preferably, the optical path returning means is arranged for each of optical paths of the light components of the respective wavelengths, which are output from the second spatial wavelength branch means, and a distance between a diffraction position of a light component having a specific wavelength on the second spatial wavelength branch means and the optical path returning means corresponding to this light component is different from a distance between a diffraction position of a light component having another wavelength on the second spatial wavelength branch means and the optical path returning means corresponding to this light component.
In this case, since the optical path length of a light component having a specific wavelength in the optical signal processor is different from that of a light component having another wavelength, chromatic dispersion in these light components can be adjusted.
Also, in the optical signal processor of the present invention, preferably, the optical path returning means is arranged for each of optical paths of the light components of the respective wavelengths, which are output from the second spatial wavelength branch means, and a position at which the optical path returning means corresponding to each wavelength is arranged can be changed in a direction of optical path. In this case, the chromatic dispersion adjusting amount can be changed.